1. Field of the Invention
The present invention relates to a slip assembly for anchoring a packer assembly or the like in a well bore.
2. Description of the Prior Art
Slip assemblies are utilized in downhole tools, such as packer assemblies, bridge plugs, liner hangers, and the like, to grasp the interior wall of a well conduit to secure or anchor the tool. Thus anchored, the tool cannot be moved longitudinally upward or downward with respect to the conduit.
One form of slip assembly is designed to be permanently anchored on the well conduit, such as that which is shown in U.S. Pat. No. 4,153,109 issued to A. J. Szescila. There is shown a packer having upper and lower slip assemblies. Each slip assembly surrounds the central body of the packer and has external teeth which are to engage the well casing. The lower slip assembly has an internal expander surface which tapers in an inward and downward direction and engages a companion externally tapered surface on a lower expander secured to the body of the packer by one or more shear screws threaded in the expander and received within a peripheral groove in the body. The slip assembly has circumferentially spaced weakened sections formed therein such that relative downward shifting of the lower expander with the slip assembly causes the slip assembly to break at the weakened sections into a plurality of slip elements. These slip elements are then expanded outwardly into anchoring engagement with the well casing.
The upper end of the lower expander bears against a packing surrounding the tool body and the upper end of the packing bears against the lower end of an upper expander having a tapered surface inclined in an upward and inward direction. The tapered surface engages a companion internal tapered surface in an upper slip ring which also has weakened sections. The upper slip ring breaks into slip segments upon relative upward wedging of the upper expander within the slip assembly. These segments then shift outwardly into anchoring engagement with the wall of the well casing, or other conduit. Thus, the packer is permanently anchored with the upper slip segments preventing upward movement and the lower slip segments preventing downward movement.
Oftentimes, it is necessary or desirable to run and emplace within such a conduit a well tool which, upon completion of a remedial or other activity, may be retrieved from such emplacement, for subsequent reuse. Such a tool will, of necessity, require the use of an anchoring means, such as a slip assembly, which may be disengaged from anchoring position relative to the conduit.
One disadvantage of both permanent and retrievable prior art slip assemblies is that the tool being anchored is radially loaded. The slip segments bear against the expanders which, in turn, bear against the tool body. Such loading can deform the expanders and/or the tool body. The present invention provides a slip assembly which, when shifted to the set position, the slip elements do not bear on an expander ring. Instead, the slip elements bear against each other in the tangential direction. Therefore, the radial loading problems associated with the prior art slip assemblies are substantially eliminated by the present invention.
Upon removal from the well, the slip assembly of this invention is ready for re-insertion and reuse, if provided in the preferred retrievable form.